With the ever expanding need for high-speed information transfer at low cost, parallel optoelectronic data links have become increasingly attractive. A crucial component in such a link is the optical subassembly (OSA) which provides the interface between the optically active chip (lasers or LEDs for the transmitter; detectors for the receiver) and the ferrule carrying the terminated fibers. The OSA must consist of accurately aligned precision parts which permit the optical power emanating from the laser(s) to be efficiently transferred to the fiber(s) for the transmitter optical subassembly (TOSA), or the optical power emanating from the fiber(s) to be efficiently transferred to the detector(s) for the receiver optical subassembly (ROSA). These parts must be fabricated by techniques which render them inexpensive, but which maintain the required accuracy. One of the components of the OSA which requires the most careful design is the optical coupler. For the case of a single-channel (non-parallel) link, the optical coupler is typically a lens which is correctly designed and positioned to give the maximum useable coupling efficiency (CE) between the optical fiber and the optically active chip (see, e.g., H. van Tongeren, "Packaging of Long-Wavelength Fibre Optic Communication Lasers", Phillips J. Res., vol. 45, pp. 243-254, 1990).
In some applications, it is necessary to bend the light path by 90 degrees between the optical fiber and the active chip. A typical reason for such a bend is the necessity to maintain the fiber axis parallel to the substrate supporting the optically active chip (ultimately the card on which the optically active chip resides), while the light emanating from the chip (transmitter) or impinging on it (detector) is perpendicular to the substrate. One known solution to this problem is represented by an assembly comprising a prism or mirror and a suitably positioned lens, so that the light can be both focussed and redirected properly. See, e.g., A. J. Heiney et al, "Design and Characterization of a Novel Fiber Optic Coupling Device for Data Communication Applications", 43d Electronic Components & Technology Conference, Orlando FL, May 1993, post-deadline paper.
While the lens-prism/mirror solution may be acceptable for a single-channel link, low-cost fabrication of optical couplers using this approach is impractical for a parallel link, particularly when the channel-channel period (i.e., distance from a point in one channel to a corresponding point in an adjacent channel) is about 500 microns or smaller. It becomes very difficult to make such a small-scale lens array at low cost because machining methods do not permit precise delineation of the optically smooth, ultra-small radius surfaces needed to make such tiny lenses (whether the lens itself or a mold used to make the lens is being considered). Although special techniques have been employed to make lens arrays (N. F. Borrelli and D. L. Morse, "Microlens Arrays Produced by a Photolytic Technique", Applied Optics, vol. 27, pp. 476-479, 1988.), such techniques do not permit low-cost fabrication of small scale lens arrays which are required for parallel optoelectronic data links.
Thus, it is clear that a need has arisen for an inexpensive optical array capable of directing light from a source element to a receiving element.